   (throw "unimplemented")
   #_(instance? clojure.lang.IChunkedSeq s))
 
-#_(defn concat
+(defn concat
     "Returns a lazy seq representing the concatenation of the elements in the supplied colls."
     {:added "1.0"
      :static true}

   :inline (fn [x y] `(. clojure.lang.Util compare ~x ~y))
   :added "1.0"}
  [x y]
  (throw "unimplemented")
  #_(. clojure.lang.Util (compare x y)))


                        (cat (first zs) (next zs)))))))]
       (cat (concat x y) zs))))

;;;;;;;;;;;;;;;;at this point all the support for syntax-quote exists;;;;;;;;;;;;;;;;;;;;;;
(defmacro delay
  "Takes a body of expressions and yields a Delay object that will
